A semiconductor manufacturing equipment such as an etching equipment, a CVD equipment or a sputtering equipment performs a process treatment such as an etching or deposition of a thin membrane in a chamber. There is a case where a plurality of chambers are connected to each other in the equipments. FIG. 1 illustrates a cross sectional view of a connection portion of two chambers disclosed in Japanese Patent Application Publication No. 5-211136. A first connection hole 12 of a first chamber 10 is connected to a second connection hole 22 of a second chamber 20. An O-ring 30 is provided between the first chamber 10 and the second chamber 20 in order to maintain vacuum in the two chambers. The O-ring 30 separates the two chambers from outside air.
However, gas or plasma in the first chamber 10 or in the second chamber 20 may cause a degradation of the O-ring, with the structure shown in FIG. 1. Therefore, the O-ring is often replaced. In particular, a quantity of the plasma reaching the O-ring is large because the plasma density is high, in a case where the first chamber 10 is a chamber for high-density plasma treatment. Therefore, the O-ring is easy to be degraded.